Support of DynamicObject or IDictionary<string, object> as context object

[tomasceleda]

If I run

var values = new ServiceExample2() { { "X", 1 }, { "Y", 2 } };
int result = context.Execute<int>("X + Y", values);

where ServiceExample2 is inherits from Dictionary<string, object> it works as expected. When it implements IDictionary<string, object> or inherits DynamicObject and implements the properties dynamically, it throws NullReferenceException.

Is there some other way how to run on object with has not the properties known at compile time?

Thanks

[JonathanMagnan]

Hello @tomasceleda ,

There is a lot of way to do it.

For example: https://dotnetfiddle.net/zclC3l

// ExpandoObject
{
	dynamic dynamicObj = new ExpandoObject();
	dynamicObj.X = 1;
	dynamicObj.Y = 2;

	Console.WriteLine(Eval.Execute<int>("X + Y", dynamicObj));
}

// VariableFactory
{
	var context = new EvalContext();
	context.VariableFactory = arg => {
		if(arg.Name == "X")
		{
			arg.Value = 1;
			arg.IsHandled = true;
		}
		else if (arg.Name == "Y")
		{
			arg.Value = 2;
			arg.IsHandled = true;
		}
	};
	
	Console.WriteLine(context.Execute<int>("X + Y"));
}

We will look about your both scenario to see why it throw an error.

Best Regards,

Jonathan

[TehWardy]

Interesting ... I hit this ...
https://stackoverflow.com/questions/53104874/querying-dynamic-data#53114267

Apart from the typo in my query code (referring to properties that don't exist I found that the problem was much the same.

I'm using Eval like this ...

public static class ObjectQueryExtensions
{
    static ObjectQueryExtensions()
    {
        EvalManager.DefaultContext.IncludeMemberFromAllParameters = true;
    }

    public static TResult Query<T, TResult>(this T source, Query query)
    {
        var code = query.ToCSharp();
        var result = Eval.Execute<object>(code, source);
        return JsonConvert.DeserializeObject<TResult>(JsonConvert.SerializeObject(result));
    }
}

... by doing the json bit at the end I can "not worry about selections having to create new t { }" instances during the querying process for the simple cost of a bit of cpu time (hense the reason that's there).

Query in this case is a custom thing I built to wrap around Eval, what it is is a Json based structure I can build out in my web based front end to define queries on objects.

In this case (as seen from the stackoverflow post I have a dynamic object that I built from getting data from multiple places (some items, some company data, ect) that I collected together in to my Eval context object.

Having done that I noticed using Eval in this manner must be doing something like this in the background when we use "EvalContext.IncludeMemberFromAllParameters = true" ...

IEnumerable<ExpandoObject> Items = source.Items;

Whereas if it did ...

IEnumerable<dynamic> Items = source.Items;

Then I believe this would work.
Lets also assume that for this whilst I actually have an ExpandoObject T is passed in as dynamic.

For the purpose of Eval here I think it might be "cleaner" in terms of user use case to always treat ExpandoObjects as dynamic although i have to admit I haven't really spent enough time to know for sure if that would cause unintended side effects.

[JonathanMagnan]

Hello @tomasceleda ,

This issue will be closed since we answered it.

We will continue the @TehWardy request on the newly thread he created

Best Regards,

Jonathan